Valve mechanism for internal combustion engine

A valve mechanism for an internal combustion engine, comprising:

• a first rocker arm linked and connected on a free end side thereof to one of an intake valve and an exhaust valve and supported for rocking motion on a rocker shaft;
• a second rocker arm supported for rocking motion on said rocker shaft and disposed adjacent said first rocker arm for being driven to rock by a cam;
• a cylinder formed on one of said first and second rocker arms and a first piston mounted for sliding motion in said cylinder;
• a contacting projection provided in a projecting manner on the other one of said first and second rocker arms for contacting with said first piston;
• a return spring for biasing said first piston toward a contacting position at which said first piston contacts with said contacting projection;
• and
• a second piston configured to displace, when hydraulic pressure is supplied thereto, said first piston to a non-contacting position, at which said first piston does not contact with said contacting projection, against the biasing force of said return spring,
• wherein said second piston is formed so as to have a diameter smaller than that of said first piston and provided in displacement in a direction away from said contacting projection,
• wherein said second piston is disposed so as to extend in parallel to said first piston at least when said first piston is at a non-contacting position,
• wherein said cylinder is formed on said first rocker arm and said first piston is disposed in said first rocker arm while said second piston is disposed in said rocker shaft.